Re: [PATCH v8 8/8] vpci/msix: Free MSIX resources when init_msix() fails

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Thu, Jul 24, 2025 at 01:50:06PM +0800, Jiqian Chen wrote:
> When init_msix() fails, current logic return fail and free MSIX-related
> resources in vpci_deassign_device(). But the previous new changes will
> hide MSIX capability and return success, it can't reach
> vpci_deassign_device() to remove resources if hiding success, so those
> resources must be removed in cleanup function of MSIX.

The text here is a bit convoluted IMO.  It would be clearer as:

When MSI-X initialization fails vPCI will hide the capability, but
remove of handlers and data won't be performed until the device is
deassigned.  Introduce a MSI-X cleanup hook that will be called when
initialization fails to cleanup MSI-X related hooks and free it's
associated data.

As all supported capabilities have been switched to use the cleanup
hooks call those from vpci_deassign_device() instead of open-code the
capability specific cleanup in there.

(see below for the reasoning behind the last paragrpah).

> To do that, implement cleanup function for MSIX.
> 
> Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
> ---
> cc: "Roger Pau Monné" <roger.pau@xxxxxxxxxx>
> ---
> v7->v8 changes:
> * Given the code in vpci_remove_registers() an error in the removal of
>   registers would likely imply memory corruption, at which point it's
>   best to fully disable the device. So, Rollback the last two modifications 
> of v7.
> 
> v6->v7 changes:
> * Change the pointer parameter of cleanup_msix() to be const.
> * When vpci_remove_registers() in cleanup_msix() fails, not to return
>   directly, instead try to free msix and re-add ctrl handler.
> * Pass pdev->vpci into vpci_add_register() instead of pdev->vpci->msix in
>   init_msix() since we need that every handler realize that msix is NULL
>   when msix is freed but handlers are still in there.
> 
> v5->v6 changes:
> * Change the logic to add dummy handler when !vpci->msix in cleanup_msix().
> 
> v4->v5 changes:
> * Change definition "static void cleanup_msix" to "static int cf_check 
> cleanup_msix"
>   since cleanup hook is changed to be int.
> * Add a read-only register for MSIX Control Register in the end of 
> cleanup_msix().
> 
> v3->v4 changes:
> * Change function name from fini_msix() to cleanup_msix().
> * Change to use XFREE to free vpci->msix.
> * In cleanup function, change the sequence of check and remove action 
> according to
>   init_msix().
> 
> v2->v3 changes:
> * Remove unnecessary clean operations in fini_msix().
> 
> v1->v2 changes:
> new patch.
> 
> Best regards,
> Jiqian Chen.
> ---
>  xen/drivers/vpci/msix.c | 44 ++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 43 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/drivers/vpci/msix.c b/xen/drivers/vpci/msix.c
> index eb3e7dcd1068..8ab159969da6 100644
> --- a/xen/drivers/vpci/msix.c
> +++ b/xen/drivers/vpci/msix.c
> @@ -655,6 +655,48 @@ int vpci_make_msix_hole(const struct pci_dev *pdev)
>      return 0;
>  }
>  
> +static int cf_check cleanup_msix(const struct pci_dev *pdev)
> +{
> +    int rc;
> +    struct vpci *vpci = pdev->vpci;
> +    const unsigned int msix_pos = pdev->msix_pos;
> +
> +    if ( !msix_pos )
> +        return 0;
> +
> +    rc = vpci_remove_registers(vpci, msix_control_reg(msix_pos), 2);
> +    if ( rc )
> +    {
> +        printk(XENLOG_ERR "%pd %pp: fail to remove MSIX handlers rc=%d\n",
> +               pdev->domain, &pdev->sbdf, rc);
> +        ASSERT_UNREACHABLE();
> +        return rc;
> +    }
> +
> +    if ( vpci->msix )
> +    {
> +        for ( unsigned int i = 0; i < ARRAY_SIZE(vpci->msix->table); i++ )
> +            if ( vpci->msix->table[i] )
> +                iounmap(vpci->msix->table[i]);
> +
> +        list_del(&vpci->msix->next);
> +        XFREE(vpci->msix);
> +    }
> +
> +    /*
> +     * The driver may not traverse the capability list and think device
> +     * supports MSIX by default. So here let the control register of MSIX
> +     * be Read-Only is to ensure MSIX disabled.
> +     */
> +    rc = vpci_add_register(vpci, vpci_hw_read16, NULL,
> +                           msix_control_reg(msix_pos), 2, NULL);
> +    if ( rc )
> +        printk(XENLOG_ERR "%pd %pp: fail to add MSIX ctrl handler rc=%d\n",
> +               pdev->domain, &pdev->sbdf, rc);
> +
> +    return rc;
> +}
> +
>  static int cf_check init_msix(struct pci_dev *pdev)
>  {
>      struct domain *d = pdev->domain;
> @@ -714,7 +756,7 @@ static int cf_check init_msix(struct pci_dev *pdev)
>  
>      return rc;
>  }
> -REGISTER_VPCI_CAP(MSIX, init_msix, NULL);
> +REGISTER_VPCI_CAP(MSIX, init_msix, cleanup_msix);

Don't you need to also call the cleanup hooks in
vpci_deassign_device() and remove the open-coded cleaning of MSI-X
done there?

Otherwise the code here is duplicated with the code in
vpci_deassign_device() for MSI-X cleanup (apart from it being a bit of
a layering violation to open-code the MSI-X cleanup in there).

Thanks, Roger.